Thermal alarm apparatus



NOV. 30, 1948. c, w, |NGELs 2,455,011

THERMAL ALARM APPARATUS Filed May 23, 1946 3 Sheets-Sheet 1 INVENTOR. Clarence W. lngels ATTORNEY Nov. 30. 1948. c. w. INGELS 2,455,011

THERMAL ALARM APFARATUS Filed lay 23, 1946 3 Sheets-Sheet 2 .3 a i. :5 I: E 9

. INVENTOR.

Clarence W. lngels ATTORNEY.

3 Sheets-Sheet 3 ATTORNEY Nov. 30 1948. c. w. INGELS THERMAL ALARM APPARATUS Filed May 23, 1946 and generators.

Patented Nov. 30, 1948 UNITED STATES PATENT OFFICE THERMAL ALARM APPARATUS Clarence W. Ingels, St. Albans, N. Y.

Application May 23, 1946, Serial No. 871,885

16 Claims.

This invention relates to electric equipment protective' systems and more particularly to signalling means for indicating when the temperature of electrical translating devices nearly becomes excessive. Electrical translating devices, such as electric motors, generators, and transformers, are subject to overloads, short circuits, faulty ventilation, and other condition-s which give rise to excessive temperatures that may damage the device. Existing protecting devices provide visible or audible indications when electric equipment reaches a predetermined critical temperature, such as the highest safe operating temperature of a motor, generator, or a transformer. Still other devices protect electrical equipment against excessive temperatures by shutting oil the power supply of an electric motor or removing the load from a generator or a transformer when the critical temperature is reached. Such actions, while protecting the device, in some instances are not entirely desirable and could be prevented if it were known that the critical temperature was being approached. By providing the operator of electrical equipment with knowledge that an increasing overload exists or that the temperature is approaching a dangerous value, he can decrease or release the load on the device before the critical temperature is reached, thereby reducing the temperature without complete stoppage of the device in the case of motors Furthermore, by providing the operator with knowledge that the temperature is decreasing, the load may more safely be reapplied or increased.

Therefore, it is an objectto this vention to provide signalling means which indi ates when the temperature of an electrical translating device nearly reaches a predetermined critical value.

Another object of this invention is to provide signalling means for electrical translating devices which indicates the rate of temperature increase or decrease when the temperature approaches an excessive value.

A further object of this invention is to provide an automatic safety device for shutting off the power to or removing the load from a translating device when a critical temperature is reached together with signalling means to indicate when the temperature of the translating device has nearly reached the point where the safety device will operate.

Still another object of this invention is to pro.- vide temperature indicating mean-s for translating devices that is responsive directly to the temperature of the hottest parts of the equipment and not to any variable ambient temperatures.

Other objects and advantages of the invention will be apparent from the following description and accompanying drawings in which:

Figure 1 is a fragmentary cross sectional view 2 of an electric induction motor incorporating the present invention.

Figure 2 is an enlarged cross sectional view of a part of the switch mechanism of Figure 1.

Figure 3 is a cross sectional view taken on line 3-3 of Figure 2.

Figure 4 is a cross sectional view taken on line 4-4 of Figure 2.

Figure 5 is a wiring diagram illustrating the use of my device with an electric motor.

Figure 6'is a wiring diagram illustrating the use of my device with a generator.

Figure 7 is a cross sectional view corresponding to Figure 2 of a modification of my device.

Figure 8 is a cross sectional view taken on line 8-8 of Figure '7.

Figure 9 is a cross sectional view corresponding to Figure 2 of another modification of my device.

Figure 10 is a cross sectional view taken on line Ill-J0 of Figure 9.

Referring now to Figure 1, there is shown my invention applied to a conventional three phase electric induction motor indicated generally by I. The motor is provided with a housing 2 supporting bearings 3 in which is journalled a rotor shaft l. The rotor is provided with fan blades 5. At each end of the housing are air inlet bells (5 which admit air to cool the motor. Stator windings l are mounted in the usual slots provided in the inner side of the annular laminated core 8.

The current flowing through the stator windings i develops considerable heat which is fairly rapidly dissipated from the exposed ends of the windings. That portion of the windings, however, which is embedded in the slots in the core 8 more nearly reflects the absolute temperature of the windings I and is not affected by ambient temperature variations. Accordingly, I prefer to mount my signalling apparatus in such a manner that it is directly responsive to the temperature of the embedded portions of the winding-s I.

inserted in a suitable opening 9 formed in the laminated core 8 is a member ill, preferably of copper because of its high heat conductivity, but other suitable material having high heat conductivity may be used. The member it extends into the core 8 to within close proximity of the bottom of the slots and preferably into actual contact with the electrically insulated surface of the windings 1 so that the member not only rapidly follows temperature variations of the windings, but also maintains substantially the same temperature as the windings. The member l0 projects a short distanceabove the surface of the core 8. Mounted above the member i0 is a heat dissipating or cooling member ll preferably formed of the same material as the heat conducting member. As best shown in Figures 2 and 4, the abutting faces l2 and H of both members are concavely curved both longitudinally and transversely and spaced 9. short distance apart. A

portion llof the cooling member ii enteritis 'aitially of the motor and has an end portion l5 passing through a suitable opening in the hir inlet bell 6 and prolectinginto the path oi the entering cooling air. An alternative construction, hot shown in the drawings, is extend a portion of the cooling member i i radially through a suitable opening in the motor housing 2 to project into the outside atmosphere. Both members it and. ii are enclosed in a sheath [i6 01 heat insulating material, except the lower portion of the member ill, which is in heat exchange contact with the inner portion oi the core 8 or the surface or the windings Ti, and the end portion iii of the cooling member Mfwhich projects into the path of the cooling air. The entire assembly may be fastened to the core 8 by a strap ill and screws ill, or otherwise suitably secured thereto. From the construction thus far disclosed, it can be seen that the upper face it or the member ill attains substantially the same temperature as the embedded portion of the windings 71, both because the member ill has high heat conductivity and also because the insulating sheath. it prevents the upper portion of the member [it from losing heat to the surrounding core 8. It also will be seen that the abutting face it of the cooling member 6 i will be substantially cooler than the face iii of the member iii, and similarly will tend to approach the temperature or the endportion lb projecting into the cooling air stream.

Mounted between the abutting faces (12 and is is a bi-rnetallicthermostatic strip it (Figure 2), concave incross section, and its normal position having a longitudinal curvature designed to conform to the curvature of the surface it of the member Id and to be indirect heat exchange contact therewith. Secured to the center of the strip I9 is a rod which extends radially of the core 8 through a bore in the cooling member ii to operate an electric switch, indicated generally by 2!. The means for securing the rod 20 to the strip l9 may be a nut threaded thereon, and a suitable recess 22 is provided in the member M to accommodate the nut. Mounted on top of the cooling member H is a. pair of superimposed leaf springs 23 and 24. The lower spring 23 carries an electrically insulated moving contact bar 25, while the upper spring 24 carries a pair of electrically insulated switch points 26 which are designed to complete an electrical circuit when contacted by the contact bar 25, as will be later explained. The rod 20 projects beyond the upper surface of the cooling member II and into operating engagement with the lower spring 23. A heat insulating tube 21 may be provided between the rod 20 and the wall of the bore to prevent heat from travelling from the thermostatic strip l9 to the cooling member ll.

The'normal position of the strip l9, as shown in Figure 2, allows the contact bar 25 to remain in lowered position out of contact with the switch points 26. When the thermostatic strip becomes sufficiently heated by the member ID, by reason of its double curvature it will snap into the position shown by the dotted lines in Figures 2 and 4. In this actuated position, the contact bar 25 will be raised into contact with the switch points 26, thus closing the switch 2|. By suitably constructing the bi-metallic strip IS, the temperature at which it will snap into actuated position can be predetermined. The strip is so designed that the predetermined actuating temperature is below the critical or limiting temperature of the windings I, preferably several degrees or more.

When the strip it) has snapped into actuated position, it will conform to the curvature of the lace E2 of the cooling member ii and be in heat exchange contact therewith. Accordingly, by reason or such contact and because of the larger mass oi the cooling member l i, the strip l9 will be cooled rapidly to the temperature at which it will snap back into normal position, thus lowering the contact bar 2b and opening the switch 2i. Thus, periodic opening and closing of the switch 2i will occur as long as the temperature of the windings l remains above the predetermined actuating temperature. As the temperature of the windings increases above the predetermined point, the frequency of actuation of the strip It will increase, because the higher the temperature of the face it of the member iii, the less time will be required to reheat the strip iii to its actuatin temperature.

i9 will remain in actuated position will increase slightly with the increase in temperature of the heating face it, but the time intervals when the strip is is in normal position will decrease.

The signalling apparatus of my invention is shown in the wiring diagram of Figure 5. The signalling device may be either audible, such as a bell 2t, visual, such as a lamp 28, or both. I have shown both for purposes of illustration. The bell 2d and the lamp to are connected in parallel with a suitable source of electric power and the switch 25 is interposed in one of the power lines. The power may be taken directly from the terminal board 30 of the motor i, using only two of the three terminals 30 as shown, or an independent source of electrical power, such as a battery, not shown in the drawings, may be used. To step down the voltage for the lamp 29 and bell 28, in case power is taken from the terminal board 30, either a transformer or a. suitable resistance may be used. I have shown a transformer 32 in Figure 5 and a resistance 33 in Figure 6. That portion of Figure 5 enclosed by dotted lines, indicates the apparatus located within the motor housing 2. signalling devices 28 and 29 are mounted externally thereof.

The operation of the signalling device is as follows: when the temperature of the windings I of the motor reaches the predetermined point below the critical temperature, the signalling means is intermittently operated as the strip I9 is intermittently actuated by being heated by the member in and returned to normal position by being cooled by the cooling member II. If the temperature of the windings increases beyond this predetermined point, the intervals of dead time between signals, 1. e., lighting of the lamp 29 and sounding of the M1128, will decrease.-

Thus, the operator of the motor has an indication of whether the temperature is continuing to rise above the predetermined point and is approaching the critical value. With this knowledge, the

' operator may relieve some of the load on the in temperature as well.

motor and so prevent its reaching the critical temperature and stopping it a temperature responsive safety switch is used, Not only does the signalling means serve to indicate a rise in temperature, but also it will indicate a decrease Thus when the periods of dead timebecome longer, the operator of the motor has an indication that the load safety may be reapplied, so that the motor'may be operated at all times with its highest safe load.

The invention also include automatic means for shutting off the power from the motor I if The length of time that the strip Preferably, the

. the temperature of the windings 1 reaches the curved upper and lower surfaces 3! and 3.. Positloned in the recess is a bi-metallic thermostatic strip 31, hat in cross section, but in its normal position'having'a curvature designed to conform to the curvature of the lower surface 30 of the recess 34 and to be in direct heat exchange contact therewith. The strip 11 extends out of both ends of the recess 34 through suitable openings provided in the insulating sheath I6. One pro- Jecting end of the strip extends but a short distance beyond the sheath l6 and is spring pressed by any suitable means such as a spring element 38. The other projecting end portion extends some distance beyond the sheath I8 and is pivoted short of its end as at 38 to operate 'an electric switch, indicated generally at 40. The upper side of the pivoted end of the strip 31 carries an electrically insulated contact bar ll. Mounted on a supporting member are a pair of electrically insulated switch points 42, normally contacted by the bar M to complete an electrical circuit as will be explained later.

The actuation of the strip 31 is accomplished upon a predetermined temperature in the same stead of by a double curvature of the thermostatic strip. It is to be understood, moreover, that the construction of the strip 31 and switch 40 readily may be substituted for the construction of the signalling strip l9 and switch 2i. By proper construction and adjustment, the strip 31 is designed to be actuated and snap into the position shown by the dotted lines in Figures 2 and 4 when the temperature of the windings I reaches the critical value. In this position, the contact bar H is lowered out of contact with the switch points 42, thus opening an electrical circuit. The strip 31, however, is not cooled rapidly when in its actuated position, because both the upper and lower surfaces 35 and 36 of the recess 34 are formed in the heating member ID, and accordingly are at approximately the same temperature. Hence, the strip 31 will not snap back into normal position until the temperature of the windings 1 drops below the critical point.

Referrin again to Figure 5, there is shown the wiring diagram for the temperature responsive automatic power shut off. The dot-dash lines indicate apparatus located in the motor control .box. The main switch contacts 43 of the motor are he d in closed position by the energization of a holding coil 44 which is shown as taking its power from two of the three terminals 45 on the motor control terminal board 45, although any other suitable source of power may be used. Connected in series with the holding coil 44 are a manually operable cut out or stopping switch 41 and the temperature responsive safety switch 40, which normally is closed. Connecting terminals 48 may be mounted conveniently on the motor terminal board 30. Upon actuation of the strip 31, the safety switch 40 is opened and the holding coil 44 is deenergized, thus opening the main switch contacts 43, stopping the motor.

A normally open starting switch 49 may be connected in parallel with the safety switch 40.

After having removed the load or other condition which caused the actuation of the safety switch 40, the motor may be restarted by closing the starting switch. 49 without waiting for the motor to cool sufliciently to deactuate the safety switch. Such restarting of the motor will pro. vide much more rapid cooling than if it were left to cool at rest.

Referring again to Figure 2, there is shown an alternative construction of the safety switch 40. Where my device is mounted on a generator instead of an electric motor, the safety switch 40 is designed normally to be open. Accordingly,

electrically insulated switch points 50, shown in dotted lines, are designed to be contacted by an electrically insulated contact'bar 5i, shown in dotted lines on the under side of the end of the strip 31, when the strip is actuated. The wiring diagram shown in Figure 6 shows the application of the switch 40 to remove the load from a generator.. A circuit breaker 52 connected in the generator load has its actuating coil 53 connected in series with the safety switch 40 and a source of power, which is shown as being the terminals 54 on the control terminal board 55 of the generator, although any other suitable source of power may be used. Upon actuation of the safety switch 40, the circuit breaker 52 is opened and the load removed from thegenerator. A normally open manually operable switch 56 is connected in parallel with the safety switch 40 for manual operation of the circuit breaker 52. The dotted lines of Figure 6 enclose apparatus located within'the generator housing, while the dot-dash lines enclose apparatus located or. the control terminal board 55 of the generator.

Referring now to Figures '7 and 8, there is shown a modified form of switch mechanism. The member Ill is mounted directly on the outer surface of the core 8 instead of in an opening therein. Thus, the heating member to is not directly responsive to the temperature of the winclings, but is responsive to the heat of the surface of the core, the temperature of which nearly approaches that of the windings l. The cooling member Ii, mounted in spaced relation above the heating member i6, iscooled only by the air circulating within the housing 2 of the translating device. The abutting faces El and 58 of both members are convexly curved, both longitudinally and transversely and a thermostatic strip 59 is secured at its center to either the upper face 5! or the lower faceiit. I have shown it as being secured to the face 58 of the member ill by a bolt 60. Thethermostatic strip 59, as in previously described modifications, normally conforms to the curvature of the upper surface 55 of the heating member i0 and obtains its snap action from its double curvature. Because the strip 59 is secured at its center, no end pivot or center push rod is necessary to operate a switch.

shown in dotted lines, and providing the alternatlve switch points 42, also shown in dotted lines, the strip may be positioned in a suitably shaped recess in a member l0 like the strip 31 shown in accaon strip 59 may be predetermined by proper con struction as has been described previously. I A further modification of my invention is shown in Figures 9 and 10, wherein the heating and cooling members to and M are circular in cross-section. The abutting faces 6!] and B2 or the cooling and heating members ti] and iii are concave and the thermostatic element of the signailing switch 2!] is in the form of a iii-metallic disc normally dish shaped to conform to the configuration of the face 62 of the heating mem ber iii. The thermostatic element 641 of the safety switch Gil is constructed like the strip ill of Figure 2 and is located in a passagewayor recess 65 which extends through the heating member it and has concave upper and lower surfaces til and ill. The action of the thermostatic elements [it and M corresponds to the action or elements it and 37!, respectively, shown in Figure 2. By forming the heating member ill with a circular cross section, it easily may be inserted in a drilled hole bit in the stator core 53.

Still another modification of the signalling mechanism (not shown in: the drawings) would be to eliminate the heating member iii and utihas the core ii itself as a heating member by shaping a portion of the surface of the core to correspond to any of the heating surfaces described. A suitably constructed thermostatic element then would be mounted directly between the core 8 and the superimposed cooling member.

While I have shown and described my temperature responsive signalling device as being applied specifically to electrical translating devices,

it is obvious that other applications are possible.

For example, any of the signalling devices described could be adapted to warn of the excessive heating of a bearing or the cooling fluid of a motor. Accordingly, the invention embraces all modifications and applications as fall within the spirit and scope of the appended claims.

I claim: m

1. A thermally responsive mechanism comprising; a snap acting thermally responsive element responsive to a predetermined temperature, a heat conducting member, and a cooling member adapted to be maintained at a temperature lower than the temperature of said heat conducting member, said thermally responsive element being adapted in the normal position thereof to abut against said heat conducting member for direct heat exchange therewith and in the actuated position thereof to abut against said cooling mem- Gil lid

tently actuated by being heated to said predetersaid element being adapted in the normal position thereof to be in direct heat exchange relation with said heat conducting member and in the actuated position thereof in direct heat exchange relation with said cooling member, whereby said signalling means is intermittently operated when the temperature of said heat conducting member reaches or exceeds said predetermined temperature and at a frequency which is function of the temperature or said heat con ducting member.

3. Thermally responsive electric switch means comprising a pair of metallic members having high heat conductivity mounted end to end in spaced relationship, the opposed faces of said members being oppositely curved, a snap acting thermostatic element responsive to a predetermined temperature mounted between said members, and an electric switch operable by a movable portion of said element, said element being adapted in its normal position to conform to the configuration of and'be in direct heat exchange relation with the curved end face of one of said members and in its actuated position to conform to the configuration of and be in direct heat exchange relation with the curved end face of the other of said members, the opposite end of said one member being adapted to be positioned in direct'heat exchange relation with heat producing means, the opposite end of said other member being adapted to be positioned in cooling air, whereby said electric switch is intermittently operated when the temperature of the curved end face of said one member reaches or exceeds said predetermined temperature and at a frequency which is a function of the temperature of said heat producing means.

4. The structure set forth in claim 3, in which both members are encased in heat insulating ma.- terial except for the opposite ends thereof.

5. The structure set forth in claim 3, in which the-opposed faces of the members are concavely curved.

6. The structure set forth in claim 3, in which the opposed faces of the members are convexly curved.

'7. The structure set forth in claim 3, in which the opposed faces of the members are concavely curved and a movable end portion of the thermostat extends from between said members to operate the switch.

8. The structure set-forth in claim 3,in which the opposed faces of the members are concavely curved and a switch operating rod extends from the movable portion of the thermostatic element through a bore in one of said members to opcrate the switch.

9. The structure set forth in claim 3, in which the opposed faces of the members are convexly curved and a movable end portion of the thermostatic element extends from between said members to operate the switch.

10. The structure set forth in claim 3, including a recess in said one member, a second snapacting thermostatic element responsive to a predetermined temperature higher than said first mentioned predetermined temperature mounted in said recess, and a second electric switch operable by a movable portion of said second thermostatic element.

11. Thermally responsive electric switch means comprising a member having high heat conductivity adapted to be positioned in direct heat exchange relation with heat producing means, a recess in said member having oppositely curved opposed walls, a snap-acting thermostatic element responsive to a predetermined temperature mounted in said recess, and an electric switch operable by a movable portion of said element, said element being adapted in its normal position to be in direct heat exchange relation with one of said opposed walls and in its actuated position to be in direct heat exchange relation with the other of said oppposed walls, whereby said switch is in operated position as long as the temperature of said member is at or above said predetermined temperature.

12. The combination with a translating device provided with field windings of a thermally responsive signalling means for indicating a predetermined temperature of said windings lower than the critical temperature thereof and for indicating temperature changes of said windings above said predetermined temperature, said signalling means comprising a snap-acting thermostatic element responsive to a predetermined temperature in substantially direct heat exchange relation with said windings in the normal position thereof, electric switch means operable by a movable portion of said element, electric signalling means controlled by said switch means, and a cooling member adapted to be maintained at a temperature lower than the temperature of said windings, said element in the actuated position thereof being in direct heat exchange relation with said cooling member, whereby said signalling means is intermittently operated when the temperature of said windings reaches or exceeds said predetermined temperature and at a frequency which is a function of the temperature of said windings.

13. The combination with an electric translating device having field windings and cooled by circulating air of a thermally responsive signalling means for indicating a predetermined temperature of said windings lower than the critical temperature thereof and for indicating temperature changes of said windings above said predetermined temperature, said signalling means comprising a snap-acting thermostatic element responsive to a predetermined temperature in substantially direct heat exchange relation with said windings in the normal position thereof, electric switch means operable by a movable portion of said element. electric signalling means controlled by said switch means, and a cooling member adapted to be cooled by said'circulating air, saidelement being in direct heat exchange relation with said cooling member in the actuated position thereof, wherebysaid signalling means is intermittently operated when the temperature of said windings reaches or exceeds said predetermined temperature and at a frequency greater than would be had by radiation or convection cooling alone of said element,-

said frequency being a function of the temperature of said windings.

14. The combination with a translating device ing end of said first member and having its other end positioned in the path of flow of said circulating air, the opposed ends of both of said members being oppositely curved, a snap-acting bimetallic thermostat mounted between said members, an electric switch operable by a movable portion of said thermostat, electric signalling means controlled by said switch, said thermostat being adapted in its normal position to conform to the configuration of and be in direct heat exchange relation with the curved end face of said first member and in its actuated position to conform to the configuration of and be in direct heat exchange relation with the curved end face of said second member, whereby said signalling means is intermittently operated through the actuation of said thermostat upon being heated to said predetermined temperature by said first member and cooled below said predetermined temperature by said second member, the frequency of operation of said signalling means being a function of the temperature of said windings.

15. The combination with a translating device having field windings of a thermally responsive means for indicating a predetermined temperature of said windings lower than the critical temperature thereof and for indicating temperature changes of said windings above said predetermined temperature, said means comprising: a thermostatic element, quickly deformable in response to temperatures at or above said predetermined temperature, said element, when undeformed, being in substantially direct heat exchange relation with said windings; means maintained at a temperature lower than said predetermined temperature for rapidly cooling said element, when thermally deformed, to a temperature lower than said predetermined temperature, whereby said element is intermittently deformed by winding temperatures at or above said predetermined temperature and at a frequency which is a function of said winding temperature; and electric signalling means controlled by said element.

16. A thermally responsive mechanism comprising; a heat conducting member; a cooling member adapted to bemaintained at a tempera ture lower than a predetermined temperature; a thermally actuable, temperature-sensitive element quickly movable in response to said predetermined temperature, said element being adapted in the normal position thereof to abut against said heat conducting member for direct heatexchange therewith and in the'actuated position thereof to abut against said cooling member for direct heat exchange therewith, whereby said element is intermittently actuated by being heated to said predetermined temperature by said heat conducting member and cooled below said predetermined temperature by said cooling member, the frequency of actuation being a function of the temperature of said heat conducting member.

CLARENCE W. 'INGELB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 7 Number Name Date 1,653,685 whittington Dec. 27, 1927 1,703,803 Widstrom Feb. 26, 1929 2,141,775 Varley Dec. 27, 1938 2,223,531 Putnam 3. 1940 

